The present invention relates to transport management technology, and more particularly, to a method and system of transport management in wafer fabrication.
A conventional semiconductor factory typically includes requisite fabrication tools to process semiconductor wafers for a particular purpose, employing processes such as photolithography, chemical-mechanical polishing, or chemical vapor deposition. During manufacture, the semiconductor wafer passes through a series of process steps, performed by various fabrication tools. For example, in the production of an integrated semiconductor product, the semiconductor wafer can pass through up to 600 process steps.
The wafers are typically stored in containers, such as cassettes, each of which holds up to 25 wafers. The cassettes are then loaded in carriers, such as standard mechanical interfaces (SMIFs) or front opening unified pods (FOUPs) for transport throughout the factory. A carrier may contain multiple wafer lots to undergo a fabrication task. An automated material handling system (AMHS) is employed to move carriers containing wafer lots from one location to another based on instructions from the MES in a 300 mm fab. Wafer carriers are typically input to the AMHS using automated equipment. Automated equipment is also used to remove wafer carriers using the fabrication tool loadport as the exit point, with the AMHS and/or removal equipment designed to allow several wafer carriers to accumulate near locations while preventing collisions between adjacent wafer carriers. A material transfer system (MTS) connects to a plurality of host computers and each host computer connects to a plurality of fabrication tools. An equipment automation program (EAP) is embedded in the host computer for transferring messages and issuing commands between the MTS and the fabrication tool. The MTS follows a series of standard procedural steps to issue commands to the AMHS, and the AMHS transfers wafer carriers accordingly.
In regular use, a host computer issues a carrier loading command to the MTS upon receiving a ready to load (RTL) event from a fabrication tool, and the MTS follows procedural steps to direct the AMHS to move relevant carriers to the fabrication tool loadport. After loading wafers, the fabrication tool performs a fabrication operation thereon. The host computer issues a carrier unload command to the MTS upon receiving a ready to unload (RTU) event from the fabrication tool, and the MTS directs the AMHS to move the carriers from the fabrication tool loadport.
The conventional transport process entails several limitations often associated with lack of process resource, such as control job, process job space, internal buffer capacity, or others. In one situation, a carrier may be stocked in a fabrication tool once wafer lots therein acquire insufficient control job or process job space. The AMHS removes carriers from the fabrication tool until an operator issues a carrier unload command to the MTS via the host computer, decreasing the fabrication tool utility. In another situation, a carrier containing wafer lots not having undergone a fabrication operation is cyclically loaded into and removed from a fabrication tool with internal buffer by the AMHS once the fabrication tool possesses insufficient space of the internal buffer. The AMHS stops cyclic transport until the carrier is capable of acquiring sufficient space in the internal buffer, decreasing AMHS efficacy.
In view of these limitations, a need exists for a system and method of wafer transport traffic management that preemptively determines whether the fabrication tool has access to requisite resources, thereby increasing fabrication tool and AMHS efficacy.